Model predictive control having application to distillation

a model predictive controller and distillation technology, applied in adaptive control, separation processes, instruments, etc., can solve the problems of difficult to control the liquid to vapor ratio within the column and therefore the product purity, difficult to tune the model predictive controller, and difficulty in multivariable systems, so as to achieve less volatile components

Active Publication Date: 2007-02-15
PRAXAIR TECH INC
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  • Claims
  • Application Information

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Benefits of technology

[0010] The present invention provides a method of controlling a distillation column having control valves including a reflux flow control valve to manipulate reflux flow rate to a top section of the column and at least one inlet for a feed to be separated that is situated below a reflux inlet for the reflux flow. The feed has a va

Problems solved by technology

As a result, during an upset condition caused by a change in feed composition, it can be difficult, to control the liquid to vapor ratio within the column and therefore the product purity.
Another more general problem of control is that model predictive controllers can be very difficult to tune when used in connection with certain types of systems that can incl

Method used

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  • Model predictive control having application to distillation
  • Model predictive control having application to distillation
  • Model predictive control having application to distillation

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Embodiment Construction

[0027] With reference to FIG. 1 a distillation column system 1 is illustrated that includes a distillation column 2, valve controllers 3a and 3b and a model predictive controller 4.

[0028] Distillation column 2 is designed to receive a liquid feed 10 to separate the components through distillation to produce a purified product 12 as tower overhead. Distillation column 2 consists of mass transfer elements, which in the illustration are sieve trays. The present invention, however, would be applicable to any type of column including that having random or structured packing. In a known manner, an ascending vapor phase of mixture to be separated ascends in column 2 and becomes evermore rich in the more volatile components, referred to in the art as the lighter components. A descending liquid phase contacts the ascending vapor phase through the mass transfer elements and becomes evermore rich in the less volatile components, known as the heavier components, as the liquid phase descends wi...

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Abstract

A method of controlling a distillation column having control valves to control both reflux and the vapor rate within the column. In accordance with the present invention, a temperature sensed in a top section of the column is magnified and utilized within the model predictive controller so that control is more aggressive as temperatures increase beyond a threshold temperature. Additionally, in the distillation column, or in fact in any other system in which two or more manipulated variables control two or more common controlled variables, special modeling techniques are utilized to make controller tuning easier to accomplish. In such modeling techniques, each manipulated variable is assumed to be able to have an effect on a controlled variable by a single step response model and other step response models are utilized so that the other manipulated variable(s) that also would have an effect on the same controlled variable are taken into account by the controller as feed forward variables.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of controlling a distillation column or other system by model predictive control. More particularly, the present invention relates to such a method in which temperatures in a top section of the distillation column, as utilized by the controller, are transformed to obtain more aggressive manipulation of reflux addition in columns having instability due to multiple steady-state temperature profiles. Additionally, the present invention relates to such a method that also has application systems other than distillation columns in which certain manipulated variables are utilized within the controller as feed forward variables to allow for simplified controller tuning. BACKGROUND OF THE INVENTION [0002] Model predictive control systems known as “MPC” are utilized to control a variety of industrial processes. Generally speaking, model predictive controllers operate on independent and dependent variables. Independent var...

Claims

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Application Information

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IPC IPC(8): G05B13/02
CPCB01D3/4211B01D3/4272F25J3/0295G05B13/042F25J3/04848F25J2280/50F25J3/04793
Inventor DADEBO, SOLOMON A.HANSON, THOMAS CRAIGKLEIN, FRANK J. III
Owner PRAXAIR TECH INC
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